Oil nozzle displacement prediction method and after-pressure flowback adjustment oil nozzle selection method

Abstract

The invention discloses an oil nozzle displacement prediction method and a post-pressure flowback adjusting oil nozzle selection method. The oil nozzle displacement prediction method comprises the steps that a gas-phase fluid model and a liquid-phase fluid model of the cross section of a wellhead and a gas-phase fluid model and a liquid-phase fluid model of the cross section of an oil nozzle are established respectively; generating a pressure difference model of a wellhead cross section and an oil nozzle cross section according to the gas phase fluid model and the liquid phase fluid model; converting the pressure difference model into a function of an oil nozzle outlet flow velocity variable and a pressure difference; generating an oil nozzle outlet flow prediction model according to the function of the oil nozzle outlet flow velocity variable and the pressure difference; and determining the oil nozzle outlet flow according to the oil nozzle outlet flow prediction model. By means of the scheme, accurate prediction of the liquid amount and the gas amount in the adjusting process of the low-permeability reservoir volume fracturing flow-back oil nozzle can be achieved, and effective reference data are provided for selection of the oil nozzle.

Description

Technical Field

[0001] The invention relates to the field of oil and gas development of petroleum and natural gas engineering, and in particular to a method for predicting the displacement of an oil nozzle, and also to a method for selecting an oil nozzle for post-compression flowback regulation. Background Art

[0002] In the process of oil and gas development, due to the poor physical properties of low permeability reservoirs, it is usually necessary to increase reservoir conductivity through fracturing to increase production. The production capacity of oil and gas wells after fracturing depends largely on this conductivity. During fracturing, proppant and fracturing fluid are injected into the ground through engineering means to form cracks, and before oil and gas wells are produced, the fracturing fluid needs to be returned to the ground by adjusting the soaking time and nozzle size. If the soaking time and nozzle size are inappropriate, the reservoir will be damaged and the reservoir conductivity will be reduced.

[0003] In the prior art, post-pressure flowback regulation mainly requires installing a nozzle at the wellhead to adjust the gas and liquid volumes. Since the flowback fluid usually contains two phases, gas and liquid, the existing calculation method cannot calculate the exact gas and liquid volumes under different nozzle size conditions. Under normal conditions, only the historical experience of the block can be used, and the appropriate nozzle size cannot be accurately selected, resulting in a large difference between the discharge volume and the expected volume after using an inappropriate nozzle, which in turn causes sand to be discharged and the fracture conductivity to decrease. Summary of the invention

[0004] The present invention provides a method for predicting the flow rate of a nozzle and a method for selecting a nozzle for adjusting flowback after fracturing, so as to achieve accurate prediction of the liquid volume and gas volume during the adjustment of the flowback nozzle in volume fracturing of a low permeability oil reservoir, and provide effective reference data for the selection of the nozzle.

[0005] To this end, the present invention provides the following technical solutions:

[0006] A method for predicting the displacement of a fuel nozzle, the method comprising:

[0007] Establishing gas phase fluid model and liquid phase fluid model of the wellhead cross section, and gas phase fluid model and liquid phase fluid model of the nozzle cross section respectively;

[0008] Generate a pressure difference model of a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model;

[0009] Converting the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference;

[0010] Generate a flow prediction model at the nozzle outlet according to a function of the nozzle outlet flow velocity variable and the pressure difference;

[0011] The flow rate at the nozzle outlet is determined according to the nozzle outlet flow rate prediction model.

[0012] Optionally, the establishing of the gas phase fluid model and the liquid phase fluid model of the wellhead cross section, and the gas phase fluid model and the liquid phase fluid model of the nozzle cross section respectively comprises:

[0013] Establish the physical model of the gas-liquid two-phase flow nozzle wellhead structure;

[0014] According to the physical model, a gas phase fluid model and a liquid phase fluid model of the wellhead cross section, and a gas phase fluid model and a liquid phase fluid model of the oil nozzle cross section are respectively established.

[0015] Optionally, the oil and gas two-phase fluid in the physical model has the following relationship:

[0016] The flow process of fluid in the wellbore and the flow process of fluid in the oil nozzle are one-dimensional flow;

[0017] The single-phase flow rate at any position of the wellbore and nozzle is equal;

[0018] When the two-phase fluid passes through the nozzle, the density of the gas and liquid phases remains unchanged;

[0019] The cross-sectional air content is the same for different cross sections;

[0020] The pressure at each point on the same cross section is the same;

[0021] For the same cross section, the flow velocity of the same phase fluid is the same;

[0022] The velocity ratio of the two-phase fluid through the surface pipeline and the nozzle is the same.

[0023] Optionally, both the gas phase fluid model and the liquid phase fluid model are represented by Bernoulli's equation.

[0024] Optionally, generating a pressure difference model of a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model comprises:

[0025] Determine a pressure difference calculation formula for a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model;

[0026] Establishing a fluid continuity equation according to the fluid continuity;

[0027] The fluid continuity equation and the pressure difference calculation formula are used to generate a pressure difference model of the wellhead cross section and the nozzle cross section.

[0028] Optionally, converting the pressure difference model into a function of nozzle outlet flow rate variable and pressure difference comprises:

[0029] Determine a slip ratio parameter between the two phases, wherein the slip ratio parameter is used to characterize the slip between the two phases;

[0030] The pressure difference model is converted into a function of the nozzle outlet flow velocity variable and the pressure difference according to the sliding speed ratio parameter.

[0031] Optionally, generating a flow prediction model at the nozzle outlet according to a function of the nozzle outlet flow velocity variable and the pressure difference comprises:

[0032] Determine the relationship between cross-sectional air content, volumetric air content and sliding speed ratio;

[0033] A flow prediction model at the nozzle outlet is generated according to the relationship and a function of the nozzle outlet flow velocity variable and the pressure difference.

[0034] Optionally, the flow prediction model at the nozzle outlet includes: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet.

[0035] Optionally, the method further comprises:

[0036] Determining a relationship between the flow rate and pressure at the nozzle outlet according to a function of the nozzle outlet flow rate variable and the pressure difference;

[0037] According to the relationship between the flow velocity and pressure at the nozzle outlet and the two-phase fluid total volume flow prediction model, a total volume flow model of the two-phase fluid at the nozzle outlet is established;

[0038] According to the relationship between the flow velocity and pressure at the nozzle outlet and the liquid flow prediction model, a volume flow model of the liquid at the nozzle outlet is established;

[0039] Establishing a volume flow model of gas at the nozzle outlet according to the total volume flow model of the two-phase fluid at the nozzle outlet and the volume flow model of the liquid at the nozzle outlet;

[0040] The gas flow prediction model is corrected according to the volume flow model of the gas at the nozzle outlet.

[0041] A method for selecting a post-pressure flowback regulating nozzle, the method comprising:

[0042] The above-mentioned nozzle displacement prediction method is used to predict the flow rate at the nozzle outlet after the pressure return adjustment;

[0043] Determine the nozzle parameters according to the flow rate at the nozzle outlet;

[0044] Select the nozzle according to the nozzle parameters.

[0045] The method for predicting the nozzle displacement under gas-liquid two-phase conditions provided by the present invention respectively establishes a gas phase fluid model and a liquid phase fluid model of the wellhead cross section, and a gas phase fluid model and a liquid phase fluid model of the nozzle cross section, and utilizes these models to generate a pressure difference model of the wellhead cross section and the nozzle cross section, and then converts the pressure difference model into an outlet flow rate variable function, and generates a flow prediction model at the nozzle outlet according to the outlet flow rate variable function, so as to realize accurate calculation of gas volume and liquid volume under different nozzles, different gas-liquid ratios and different pressure conditions, and then accurately calculates the gas volume and liquid volume before adjusting the return nozzle, so as to prevent the occurrence of reservoir damage caused by improper nozzle selection.

[0046] Furthermore, considering the influence of gas in different states on the accuracy of gas flow calculation, a volume flow model of the gas at the nozzle inlet is established, and the gas flow prediction model is corrected using the volume flow model to make the corrected gas flow prediction model more accurate.

[0047] The method for selecting a post-fracturing flowback regulation nozzle provided by the present invention utilizes the above-mentioned nozzle displacement prediction method to predict the flow rate at the nozzle outlet under post-fracturing flowback regulation, determines the nozzle parameters according to the flow rate at the nozzle outlet, and selects the nozzle according to the determined nozzle parameters, so that the nozzle can better adapt to the current fracturing flowback requirements of low permeability oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the method for predicting the nozzle displacement provided by the present invention;

[0049] Figure 2 It is a schematic diagram of the physical model of the gas-liquid two-phase flow nozzle wellhead structure;

[0050] Figure 3 It is a flow chart of the gas flow prediction model in the method of the present invention;

[0051] Figure 4 It is a comparison chart of the actual flowback volume and the simulated flowback volume calculation results of a well fracturing fluid flowback stage;

[0052] Figure 5 The present invention provides a flow chart of a method for selecting a post-pressure return flow regulating nozzle. DETAILED DESCRIPTION

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0054] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not therefore limited to the following embodiments.

[0055] In view of the problem that in the prior art, the gas and liquid volumes after replacing the nozzle cannot be accurately calculated during post-pressure flowback, resulting in improper nozzle selection and affecting the reservoir conductivity, the present invention provides a nozzle displacement prediction method and a post-pressure flowback regulating nozzle selection method, establishes a gas-liquid two-phase nozzle flow model, and realizes accurate calculation of gas and liquid volumes under different nozzles, different gas-liquid ratios and different pressure conditions.

[0056] like Figure 1 FIG. 1 is a flow chart of a method for predicting the nozzle displacement provided by the present invention, comprising the following steps:

[0057] Step 101 , respectively establishing a gas phase fluid model and a liquid phase fluid model of a wellhead cross section, and a gas phase fluid model and a liquid phase fluid model of a nozzle cross section.

[0058] Combine the following Figure 2 The schematic diagram of the physical model of the gas-liquid two-phase flow nozzle wellhead structure shown in the figure illustrates the principles of establishing the above models.

[0059] based on Figure 2 In the physical model shown, the gas-liquid two-phase flow satisfies the following oil-gas two-phase fluid relationship:

[0060] The flow process of fluid in the wellbore and the flow process of fluid in the oil nozzle are one-dimensional flow;

[0061] The single-phase flow rate at any position of the wellbore and nozzle is equal;

[0062] When the two-phase fluid passes through the nozzle, the density of the gas and liquid phases remains unchanged;

[0063] The cross-sectional air content is the same for different cross sections;

[0064] The pressure at each point on the same cross section is the same;

[0065] For the same cross section, the flow velocity of the same phase fluid is the same;

[0066] The velocity ratio of the two-phase fluids through the surface pipeline and the nozzle is the same;

[0067] Both gas and liquid single-phase fluids satisfy the Bernoulli equation conditions.

[0068] In the embodiment of the present invention, the gas phase fluid model and the liquid phase fluid model can be represented by Bernoulli equations.

[0069] The Bernoulli equation, also known as the steady flow energy equation, is a dynamic equation for the steady flow of an ideal fluid. It means that when the viscosity loss of the fluid is ignored, the sum of the pressure potential energy, kinetic energy and potential energy at any two points on the streamline remains unchanged.

[0070] Bernoulli's principle is stated as:

[0071]

[0072] Where P is the pressure at a measuring point in the fluid, v is the flow velocity of the fluid at the measuring point, ρ is the fluid density, g is the acceleration due to gravity, h is the height of the measuring point, and C is a constant.

[0073] correspond Figure 2 In the physical model shown, the gas-liquid two-phase flow can be approximated as two single-phase fluids flowing separately, and each phase of the fluid flows at a uniform speed in stages. Figure 2 The model shown is suitable for analyzing laminar flow, wavy flow and annular flow with low mass flow rate.

[0074] Based on the above theory, the Bernoulli equations of gas-liquid two-phase fluid are established at the two sections a-a1 and b-b1 respectively.

[0075] The Bernoulli equation for gas phase fluid is:

[0076]

[0077] The Bernoulli equation for liquid phase fluid is:

[0078]

[0079] Where:

[0080] z3 is the position head at the a-a1 section (i.e., the height of the calculation point from the reference surface), in m, z4 is the position head at the b-b1 section, in m;

[0081] β is the air void fraction, dimensionless;

[0082] λ is the friction coefficient, dimensionless;

[0083] p3 and p4 are the pressures of the fluid at the a-a1 section and b-b1 section respectively;

[0084] v 3g 、v 4g are the flow rates of the gas phase fluid at the a-a1 section and the b-b1 section, in m / s; v 3l 、v 4l are the flow rates of the liquid phase fluid at the a-a1 section and the b-b1 section, respectively, in m / s;

[0085] ρg , l are the fluid densities of the gas phase fluid and the liquid phase fluid, respectively.

[0086] Among them, the solution method of the friction coefficient λ needs to be based on the fluid Reynolds number R e The Reynolds number is a dimensionless number that can be used to characterize the flow of a fluid. The Reynolds number can be used to distinguish whether the flow of a fluid is laminar or turbulent, and can also be used to determine the resistance encountered by an object flowing in a fluid.

[0087] Rayleigh number R e The calculation formula is as follows:

[0088] Assuming full pipe flow, determine the flow pattern and first calculate the Rayleigh number R e :

[0089]

[0090] Where Re is the Reynolds number, dimensionless; v is the velocity of the fluid at a certain measuring point, m / s; ρ is the fluid density, kg / m 3 ; μ is the viscosity coefficient of the fluid, mPa·s; d is a characteristic length, m. For example, if the fluid flows through a circular pipe, d is the equivalent diameter of the pipe.

[0091] If R e ≤2000, the flow pattern is laminar flow, and the hydraulic friction coefficient along the flow is:

[0092]

[0093] If R e >2000, the flow pattern is turbulent, which can be divided into three cases, that is, three regions, namely:

[0094] if but

[0095]

[0096] if but

[0097]

[0098] if but

[0099]

[0100] in,

[0101] Where δ is the laminar bottom layer, l is the length in m; Δ is the absolute roughness, which can be obtained by looking up the table. The general oil pipeline is 0.14~0.15mm.

[0102] In addition, the partitioning results can also be verified by the following method, that is: when δ≥Δ, it is a hydraulically smooth pipe; when δ<Δ, it is a hydraulically rough pipe.

[0103] Step 102: Generate a pressure difference model of a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model.

[0104] Specifically, according to the gas phase fluid model and the liquid phase fluid model, the pressure difference calculation formula of the wellhead cross section and the nozzle cross section is determined; the fluid continuity equation is established according to the fluid continuity; and then the fluid continuity equation and the pressure difference calculation formula are used to generate the pressure difference model of the wellhead cross section and the nozzle cross section.

[0105] Reference Figure 2 , the fluid continuity equation is as follows:

[0106] v 3g A3=v 4g A4 (8)

[0107] v 3l A3=v 4l A4 (9)

[0108]

[0109]

[0110] Where d and D are the diameters before and after the nozzle, respectively, in meters; A3 and A4 are the cross-sectional areas at the a-a1 section and the b-b1 section, respectively.

[0111] According to the above formulas (1) and (2), the pressure difference calculation formula between the wellhead cross section and the nozzle cross section can be obtained:

[0112]

[0113] Substituting the continuity equation into (12) we obtain:

[0114]

[0115] The above equation (13) is the pressure difference model.

[0116] Step 103: convert the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference.

[0117] Specifically, a slip ratio parameter between the two phases is determined, wherein the slip ratio parameter is used to characterize the slip between the two phases; and the pressure difference model is converted into a function of the nozzle outlet flow velocity variable and the pressure difference according to the slip ratio parameter.

[0118] Continue to refer to Figure 2 , the expression of slip ratio s is:

[0119]

[0120] Where s is the sliding speed ratio, dimensionless.

[0121] Substituting the above sliding speed ratio into the above equation (13), and expressing the model pressure difference with the outlet flow rate variable, the function of the nozzle outlet flow rate variable and the pressure difference can be obtained:

[0122]

[0123]

[0124] Where Δp is the pressure difference between the a-a1 section and the b-b1 section, and B is the intermediate calculation equation.

[0125] Step 104: Generate a flow prediction model at the nozzle outlet according to the function of the nozzle outlet flow velocity variable and the pressure difference.

[0126] Specifically, the relationship between the cross-sectional air content, the volumetric air content and the sliding speed ratio can be determined, and the flow prediction model at the nozzle outlet is generated according to the relationship and the function of the nozzle outlet flow velocity variable and the pressure difference.

[0127] Continue to refer to Figure 2 , the calculation method of cross-sectional air content, volumetric air content and sliding speed ratio is:

[0128]

[0129] Where s is the sliding speed ratio, dimensionless; α is the cross-sectional air content, dimensionless; β is the volumetric air content, dimensionless.

[0130] Substitute the above relationship (17) into the function (15) of the nozzle outlet flow rate variable and the pressure difference to generate a flow prediction model at the nozzle outlet.

[0131] In an embodiment of the present invention, the flow prediction model at the nozzle outlet may include the following three models, namely: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet, which are respectively expressed as follows:

[0132] The prediction model of the total volume flow rate of two-phase fluid at the nozzle outlet is:

[0133] Q 4total =A4αv 4g +A4(1-α)v 4l (18)

[0134] The liquid flow prediction model at the nozzle outlet is:

[0135] Q 4l =A4(1-α)v 4l (19)

[0136] The gas flow prediction model at the nozzle outlet is:

[0137] Q 4g =A4αv 4g (20)

[0138] Where: Q 4total is the total volume flow rate of the two-phase fluid, in m 3 / s;Q 4l is the total volume flow rate of the liquid, in m 3 / s;Q 4g is the total volume flow rate of gas, in m 3 / s.

[0139] Step 105, determining the flow rate at the nozzle outlet according to the nozzle outlet flow rate prediction model.

[0140] The method for predicting the nozzle displacement under gas-liquid two-phase conditions provided by the present invention respectively establishes a gas phase fluid model and a liquid phase fluid model of the wellhead cross section, and a gas phase fluid model and a liquid phase fluid model of the nozzle cross section, and utilizes these models to generate a pressure difference model of the wellhead cross section and the nozzle cross section, and then converts the pressure difference model into an outlet flow rate variable function, and generates a flow prediction model at the nozzle outlet according to the outlet flow rate variable function, so as to realize accurate calculation of gas volume and liquid volume under different nozzles, different gas-liquid ratios and different pressure conditions, and then accurately calculates the gas volume and liquid volume before adjusting the return nozzle, so as to prevent the occurrence of reservoir damage caused by improper nozzle selection.

[0141] Taking into account the impact of gases in different states on the accuracy of gas flow calculation, in another non-limiting embodiment of the method of the present invention, a volume flow model of the gas at the nozzle inlet can be established, and the gas flow prediction model can be corrected using the volume flow model to make the corrected gas flow prediction model more accurate.

[0142] like Figure 3 FIG. 1 is a flow chart of a gas flow prediction model in the method of the present invention, comprising the following steps:

[0143] Step 301, determining a relationship between the nozzle outlet flow rate and pressure according to a function based on the outlet flow rate variable and the pressure difference.

[0144] That is, according to the above formula (15), the relationship between the flow rate and pressure at the nozzle outlet can be obtained.

[0145] Step 302: Establish a total volume flow model of the two-phase fluid at the nozzle outlet according to the relationship between the nozzle outlet flow velocity and pressure and the two-phase fluid total volume flow prediction model.

[0146] Substituting the relationship between the flow velocity and pressure at the nozzle outlet into the outlet flow expression (18), the total volume flow model of the two-phase fluid at the nozzle outlet is obtained, namely:

[0147]

[0148] Step 303: establishing a volume flow model of the liquid at the nozzle outlet according to the relationship between the nozzle outlet flow velocity and pressure and the liquid flow prediction model.

[0149] Substituting the relationship between the flow velocity and pressure at the nozzle outlet into the outlet flow expression (19), the volume flow model of the liquid at the nozzle outlet is obtained, namely:

[0150]

[0151] Step 304 , establishing a volume flow model of gas at the nozzle outlet according to the total volume flow model of the two-phase fluid at the nozzle outlet and the volume flow model of the liquid at the nozzle outlet.

[0152] Step 305: correcting the gas flow prediction model according to the volume flow model of the gas at the nozzle outlet.

[0153] The liquid phase is regarded as a Newtonian fluid, and since the inlet and outlet liquid volumes are equal, Q in the above equations (21) and (22) is 4total With Q 4l The difference is the gas flow rate at the nozzle inlet. If you want to solve the gas flow rate of the real gas at the nozzle outlet, the equation needs to be corrected according to the gas state equation.

[0154] The gas state equation at the a-a1 and b-b1 sections in the above physical model is:

[0155] p3V3=ZnRT3 (23)

[0156] p4V4=ZnRT4 (24)

[0157] ∫p3Q 3g dt=ZnRT3 (25)

[0158] ∫p4Q4g dt=ZnRT4 (26)

[0159] Where: Z is the gas deviation factor; n is the number of moles; R is a constant; T3 and T4 are the temperatures at the a-a1 and b-b1 sections, respectively, in K.

[0160] According to equations (25) and (26), the corrected actual outlet gas flow rate is:

[0161]

[0162]

[0163]

[0164] The above formula (29) is the corrected gas flow prediction model at the nozzle outlet.

[0165] Compared with the conventional nozzle flow calculation method, the scheme of the present invention can accurately calculate the gas volume and liquid volume under different gas content, different nozzle sizes and different pressure conditions, and realize the effective prediction of gas and gas displacement under different nozzle sizes during the flowback process.

[0166] The model was verified using the data of a real fracturing flowback well in a low permeability block LX1. The data of the well’s pipeline geometry parameters, fluid physical properties parameters, reservoir physical properties parameters, etc. are shown in Table 1.

[0167] Table 1

[0168]

[0169] The well started fracturing on April 28, 2022, and fracturing fluid flowback began 4 days after the well was sealed. The actual flowback volume of the fracturing fluid flowback stage of the well was compared with the simulated flowback volume calculation results. Figure 4 .

[0170] During the two-phase fluid flowback process, the fluid pressure decreases, and the phase parameters of the fluid change accordingly, resulting in bubbling flow and slug flow patterns in the pipeline. When the fluid pressure at each node in the wellbore decreases, the gas volume increases. At this time, the gas is located at the center of the pipeline and the liquid is at the wall of the pipeline. The gas content of the pipeline will fluctuate, resulting in fluctuations in the outlet liquid volume. Figure 4 It can be seen that the simulated production runs through the real production line, indicating that the simulated discharge volume in this stage is close to the real cumulative return volume; the simulated average return volume in this stage is 28.31m 3 / d, the actual average return flow is 29.32m 3 / d, the error is about 3.4%. In the process of gas-liquid two-phase flow, this accuracy fully meets the field measurement requirements (error within 5%). Therefore, in the case of unstable gas volume, the calculation result is still accurate and can be used to predict the wellhead return liquid volume, gas volume and total flow.

[0171] Figure 4 The simulated production in the results shows a concave decline, which is consistent with the reservoir fluid seepage law and the Arps (Advanced Regional Prediction System) production decline law.

[0172] Correspondingly, the present invention also provides a method for selecting a post-pressure return flow regulation nozzle, which uses the above-mentioned nozzle displacement prediction method to predict the flow at the nozzle outlet under the post-pressure return flow regulation, and selects a suitable nozzle according to the prediction result.

[0173] like Figure 5 As shown, it is a flow chart of a method for selecting a post-pressure return flow regulating nozzle provided by the present invention, which comprises the following steps:

[0174] Step 501, predicting the post-pressure backflow to adjust the flow rate at the outlet of the lower nozzle.

[0175] The flow rate prediction method at the nozzle outlet can be found in the description of the previous embodiments, which will not be repeated here.

[0176] Step 502, determining nozzle parameters according to the flow rate at the nozzle outlet.

[0177] The nozzle parameters may include but are not limited to: nozzle material, caliber, structure and other parameters.

[0178] Step 503: Select a nozzle according to the nozzle parameters.

[0179] The method for selecting a post-fracturing flowback regulation nozzle provided by the present invention utilizes the above-mentioned nozzle displacement prediction method to predict the flow rate at the nozzle outlet under post-fracturing flowback regulation, determines the nozzle parameters according to the flow rate at the nozzle outlet, and selects the nozzle according to the determined nozzle parameters, so that the nozzle can better adapt to the current fracturing flowback requirements of low permeability oil reservoirs.

[0180] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0181] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. Moreover, the system embodiments described above are merely schematic, in which the modules and units described as separate components may or may not be physically separated, that is, they may be located on one network unit, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0182] The embodiments of the present invention are described in detail above. The present invention is described in detail using specific implementation methods herein. The description of the above embodiments is only used to help understand the method and system of the present invention. It is only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should belong to the scope of protection of the present invention, and the content of this specification should not be understood as limiting the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting the displacement of a fuel nozzle, characterized in that: The method comprises: Establishing gas phase fluid model and liquid phase fluid model of the wellhead cross section, and gas phase fluid model and liquid phase fluid model of the nozzle cross section respectively; Generate a pressure difference model of a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model; Converting the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference; Generate a flow prediction model at the nozzle outlet according to a function of the nozzle outlet flow velocity variable and the pressure difference; The flow rate at the nozzle outlet is determined according to the nozzle outlet flow rate prediction model.

2. The method for predicting the nozzle displacement according to claim 1, characterized in that: The gas phase fluid model and the liquid phase fluid model of the wellhead cross section and the gas phase fluid model and the liquid phase fluid model of the nozzle cross section are respectively established, including: Establish the physical model of the gas-liquid two-phase flow nozzle wellhead structure; According to the physical model, a gas phase fluid model and a liquid phase fluid model of the wellhead cross section, and a gas phase fluid model and a liquid phase fluid model of the oil nozzle cross section are respectively established.

3. The method for predicting the nozzle displacement according to claim 2, characterized in that: The oil and gas two-phase fluid in the physical model has the following relationship: The flow process of fluid in the wellbore and the flow process of fluid in the oil nozzle are one-dimensional flow; The single-phase flow rate at any position of the wellbore and nozzle is equal; When the two-phase fluid passes through the nozzle, the density of the gas and liquid phases remains unchanged; The cross-sectional air content is the same for different cross sections; The pressure at each point on the same cross section is the same; For the same cross section, the flow velocity of the same phase fluid is the same; The velocity ratio of the two-phase fluid through the surface pipeline and the nozzle is the same.

4. The method for predicting the nozzle displacement according to claim 1, characterized in that: The gas phase fluid model and the liquid phase fluid model are both represented by Bernoulli equations.

5. The method for predicting the nozzle displacement according to claim 1, characterized in that: The pressure difference model of the wellhead cross section and the nozzle cross section generated according to the gas phase fluid model and the liquid phase fluid model comprises: Determine a pressure difference calculation formula for a wellhead cross section and a nozzle cross section according to the gas phase fluid model and the liquid phase fluid model; Establishing a fluid continuity equation according to the fluid continuity; The fluid continuity equation and the pressure difference calculation formula are used to generate a pressure difference model of the wellhead cross section and the nozzle cross section.

6. The method for predicting the nozzle displacement according to any one of claims 1 to 5, characterized in that: The step of converting the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference comprises: Determine a slip ratio parameter between the two phases, wherein the slip ratio parameter is used to characterize the slip between the two phases; The pressure difference model is converted into a function of the nozzle outlet flow velocity variable and the pressure difference according to the sliding speed ratio parameter.

7. The method for predicting the nozzle displacement according to claim 6, characterized in that: The method of generating a flow prediction model at the nozzle outlet according to a function of the nozzle outlet flow velocity variable and the pressure difference comprises: Determine the relationship between cross-sectional air content, volumetric air content and sliding speed ratio; A flow prediction model at the nozzle outlet is generated according to the relationship and a function of the nozzle outlet flow velocity variable and the pressure difference.

8. The method for predicting the nozzle displacement according to claim 7, characterized in that: The flow prediction model at the nozzle outlet includes: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet.

9. The method for predicting the nozzle displacement according to claim 8, characterized in that: The method further comprises: Determining a relationship between the flow rate and pressure at the nozzle outlet according to a function of the nozzle outlet flow rate variable and the pressure difference; According to the relationship between the flow velocity and pressure at the nozzle outlet and the two-phase fluid total volume flow prediction model, a total volume flow model of the two-phase fluid at the nozzle outlet is established; According to the relationship between the flow velocity and pressure at the nozzle outlet and the liquid flow prediction model, a volume flow model of the liquid at the nozzle outlet is established; Establishing a volume flow model of gas at the nozzle outlet according to the total volume flow model of the two-phase fluid at the nozzle outlet and the volume flow model of the liquid at the nozzle outlet; The gas flow prediction model is corrected according to the volume flow model of the gas at the nozzle outlet.

10. A method for selecting a post-pressure return flow regulating nozzle, characterized in that: The method comprises: Utilize the nozzle displacement prediction method according to any one of claims 1 to 5 to predict the flow rate at the nozzle outlet after pressure return adjustment; Determine the nozzle parameters according to the flow rate at the nozzle outlet; Select the nozzle according to the nozzle parameters.

Images